This invention relates to a system for assembly of radial tires and to methods and apparatus incorporated in such system.
The basic elements of modern radial ply pneumatic tires consist of an innerliner, one or more radial plies, sidewalls, beads and fillers, etc., all combined to form a carcass, and one or more belts made of steel cord or other cord materials combined with tread stock material to form a belt-tread stock assembly. These two assemblies are then combined to form a green tire, which is subsequently vulcanized in a mold.
U.S. Pat. No. 4,402,782 issued Sep. 6, 1983 to the assignee of this application, describes a method and apparatus for constructing such radial ply pneumatic tires by producing major assemblies on two distinct and separate types of apparatus, and combining those assemblies into a green tire, which is then vulcanized in a mold.
The first assembly, referred to herein as the "first stage carcass" consists of an innerliner plus one or more body plies of rubber coated cord material, a pair of axially spaced parallel bead assemblies encompassed by layers of ply material, and side wall stock material, all of which when combined comprise a first stage assembly. These tire elements are assembled and consolidated on a cylindrical carcass building drum such that the body plies (in the case of a radial tire) have ply cords essentially parallel to the rotational axis of the building drum as the carcass is assembled thereon, e.g. extending along the cylindrical carcass. The two bead assemblies (hereinafter referred to as "beads") are anchored to the opposing axial extremities of the first stage carcass, for example by folding part of the plies inward around the respective beads, the beads being parallel one to the other and coaxial with the rotational axis of the carcass, and two layers of sidewall stock are circumferentially consolidated to the outer surface of the carcass, axially disposed one from the other and each adjacent to one of the beads. Upon completion the carcass is transformed from its cylindrical shape to that of a toroid so the radial body cords are made to assume the configuration of meridians to the rotational axis of the carcass.
The second assembly is prepared by consolidating one or more relatively nonextensible belts, of suitable cord (e.g. steel wire in the case of a steel belted tire) incorporated into uncured rubber stock, with a band of tread stock. Then the belt/tread stock assembly is consolidated with the toroidal carcass, producing a finished green radial tire carcass which is removed from the building machine and placed in a suitable mold for final shaping and vulcanization of the various rubber components, thereby forming a completed cured tire.
Conversion of the cylindrical first stage cylindrical carcass assembly to toroidal shape, and attaching the belt/tread stock assembly thereon, has been achieved in a variety of ways.
The more conventional steps are:
(1) Assembly of the first stage carcass components on a holding drum that is capable of causing the consolidated cylindrically shaped first stage carcass to be transformed into a toroidal shape and then completion of the green radial tire carcass by attaching equatorially thereon the belt and tread stock elements; this is usually referred to as the single stage process of green tire assembly; or
(2) Assembly of the first stage carcass on a conventional collapsible building drum that is incapable of transforming a cylindrical carcass to toroidal shape, and, upon completion of that cylindrical assembly, transferring same to a different drum or holding means whereby said first stage carcass is held and manipulated during its transformation to toroidal shape and the assembly of belts and tread stock thereon; this is generally referred to as the two stage process.
Present construction processes also include the alternatives of either assembling and consolidating the belts and tread stock directly on the toroidal first stage carcass, or assembling and consolidating the belts and tread stock on a separate drum and then conveying that belt-tread subassembly to a coaxial position with the toroidal shaped first stage carcass, whereupon such toroidal first stage carcass is caused to be further expanded into circumferential contact and consolidation with the inner surface of the belt-tread stock assembly.
Both of these systems, however, have a number of disadvantages. The single stage system is slow and inflexible; it suffers from down time when process components are unavailable; specification changeover is time consuming since many different equipment elements must be exchanged and/or adjusted; single stage equipment requires much expensive tooling; such systems require highly skilled and well trained operators; such systems are expensive, not very productive and they are therefore not widely used.
The two-stage process requires two distinct types of assembly equipment; (a) a carcass building machine, and (b) a second stage assembly machine. As the industry has moved from 4-ply, bias construction to radial tire construction, the old bias machines were kept and are being used as carcass builders. These machines were usually designed in the late 1950's and 1960's and they lack the precision and alignment characteristics required to allow the assembly of a precision first stage carcass. Having had the ability to build a carcass, emphasis was placed by the industry and equipment suppliers on developing second stage machinery, and there are a number of systems being used, while the development of a precision carcass assembly system has been neglected. Since carcass building requires the assembly of all of the basic components going into a radial tire except for belts and tread stock or extrusion, it takes a greater amount of time to assemble a carcass than the second stage of the radial tire. Thus, a difference in building rates exists which is difficult to overcome through scheduling schemes.
Depending on the speed of the first and second stage machines being used, as well as the different tire constructions being assembled, the ratios of carcass to second stage building often vary between two first stage machines to one second stage machine which ratio increases, in some cases, even up to 3 to 1, making it additionally difficult to plan for capacity increases.
Because of the uneven productive output of these assembly systems, in-process carcasses that are waiting to be second staged must be handled, stored and carted to second stage assembly machines which are usually located in other areas of a plant. Such handling and storage is costly due to additional labor and large amount of floor space requirements but, above all, the handling and storage adds many uncontrollable and undesirable process variables to the product. Examples are additional touching by human hands and the associated exposure to hand perspiration, dirt or greases on hands and fingers, remnants from soaps, hand wash detergents or skin creams which may be present; the exposure to airborne particles which deposit themselves on the outer surfaces of the carcass; and the unknown duration of that exposure which may be as low as one hour but which could be as long as three and four days on long weekends. Along with that exposure variable goes the fact that a surface cure will take place often due to high ambient temperatures in storage areas. All of this affects the adhesion of the green, in-process product and the final bonding being achieved by curing the tire in a mold.
Conventional carcass building machines consist of a stationary tire assembly machine and a multi-station component storage and delivery services. These machines are designed to accept a collapsible drum on which components are placed in a sequential order. These components are extracted from the different servicer positions by the operator, touched by his hands and fingers, while the pulling motion may not be uniform thus often causing noticeable cord distortions and component dislocations. Such extracted components are then cut to length by the operator using a conventional hot knife, and these manually cut components are loosely guided onto the assembly drum through the means of mechanical edge guiders. This method of component assembly is not very precise but is, above all, labor intensive and operator dependent in terms of his skills and willingness to do a good job. Cut tire analysis will confirm that builder produced splices are often one cord overlap in one area while being 5 or 6 cord overlap elsewhere.
The quality of the completed radial ply tire requires that dimensionally accurate components are precisely assembled and such precision of dimension and assembly be maintained throughout the balance of the tire manufacturing process.
State of the art second stage radial tire building machines generally consist of a bed having mounted at opposite ends thereof, spaced apart and axially aligned, a first shaft supporting a rotatable collapsible belt building drum and a second shaft supporting a rotatable tire building drum which receives a first stage carcass. On that drum a carcass is transformed from cylindrical to toroidal shape, united with a belt-tread stock assembly formed on the belt building drum and then rotated about its axis while final consolidation is accomplished by stitching.